U.S. patent application number 12/562339 was filed with the patent office on 2010-04-01 for method for detection of abnormal combustion for internal combustion engines.
Invention is credited to Dominique AUCLAIR, Laurent DUVAL, Alexandre PAGOT, Jean-Marc ZACCARDI.
Application Number | 20100077992 12/562339 |
Document ID | / |
Family ID | 40640305 |
Filed Date | 2010-04-01 |
United States Patent
Application |
20100077992 |
Kind Code |
A1 |
AUCLAIR; Dominique ; et
al. |
April 1, 2010 |
Method for Detection of Abnormal Combustion for Internal Combustion
Engines
Abstract
A method for detection of abnormal combustion for internal
combustion engines is disclosed. A physical model is chosen that
describes, as a function of the angle a of rotation of the engine
crankshaft, the development of pressure in the cylinder during
combustion without any pre-ignition phenomenon. The cylinder
pressure P.sub.e(.alpha.) is estimated using this model and the
intake pressure is measured. The beginning of abnormal combustion
is detected by comparing a first value of a variable calculated
using the measurement of the cylinder pressure, to a second value
of the variable calculated using the estimation of the cylinder
pressure. The amplitude of the pre-ignition is determined by
repeating these steps for a defined number of crankshaft angles.
Then the progress of the abnormal combustion detected in the
combustion chamber is controlled as a function of the amplitude of
the pre-ignition phenomenon.
Inventors: |
AUCLAIR; Dominique;
(Villiers-sur-Marne, FR) ; DUVAL; Laurent;
(Nanterre, FR) ; PAGOT; Alexandre;
(Rueil-Malmaison, FR) ; ZACCARDI; Jean-Marc;
(Seynod, FR) |
Correspondence
Address: |
ANTONELLI, TERRY, STOUT & KRAUS, LLP
1300 NORTH SEVENTEENTH STREET, SUITE 1800
ARLINGTON
VA
22209-3873
US
|
Family ID: |
40640305 |
Appl. No.: |
12/562339 |
Filed: |
September 18, 2009 |
Current U.S.
Class: |
123/435 ;
701/111 |
Current CPC
Class: |
F02D 19/12 20130101;
F02D 41/402 20130101; F02D 35/023 20130101; F02D 35/024 20130101;
F02D 41/0025 20130101 |
Class at
Publication: |
123/435 ;
701/111 |
International
Class: |
F02M 7/00 20060101
F02M007/00; G06F 19/00 20060101 G06F019/00 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 18, 2008 |
FR |
08/05.132 |
Claims
1-10. (canceled)
11. A method for controlling the combustion of a supercharged
internal combustion engine with controlled ignition, in which
abnormal combustion is detected in a combustion chamber of at least
one cylinder of the engine by a continuous measurement of the
pressure inside the cylinder, comprising: a) choosing a physical
model describing, as a function of the angle of rotation of the
crankshaft of the engine, development of pressure in the at least
one cylinder during one combustion without any pre-ignition; b)
estimating a cylinder pressure, starting from the model and the
measurement of intake pressure to the at least one cylinder; c)
detecting a start of the abnormal combustion by comparing at least
one first value of a variable calculated using measurement of
pressure in the at least one cylinder and at least one second value
of the variable calculated using an estimation of the pressure in
the at least one cylinder; d) determining an amplitude of
pre-ignition by repeating steps b) and c) for a number of
crankshaft angles; and e) controlling progress of the abnormal
combustion detected in the combustion chamber according to the
amplitude of the pre-ignition.
12. A method according to claim 11, wherein: the physical model
describes a variation in pressure in the at least one cylinder as a
function of the intake pressure and volume of the combustion
chamber of the at least one cylinder.
13. A method according to claim 11, wherein: progress of the
abnormal combustion is controlled by introducing into the
combustion chamber an agent containing fuel, water, or carbon
dioxide.
14. A method according to claim 12, wherein: progress of the
abnormal combustion is controlled by introducing into the
combustion chamber an agent containing fuel, water, or carbon
dioxide.
15. A method according to claim 11, wherein: progress of the
abnormal combustion is controlled by causing pressure to drop in
the combustion chamber.
16. A method according to claim 12, wherein: progress of the
abnormal combustion is controlled by causing pressure to drop in
the combustion chamber.
17. A method according to claim 11, wherein: progress of the
abnormal combustion is controlled by opening at least one
additional valve causing pressure to dip in the combustion
chamber.
18. A method according to claim 12, wherein: progress of the
abnormal combustion is controlled by opening at least one
additional valve causing pressure to dip in the combustion
chamber.
19. A method according to claim 11, wherein: progress of the
abnormal combustion is controlled by opening at least one valve to
cause pressure to drop in the combustion chamber.
20. A method according to claim 12, wherein: progress of the
abnormal combustion is controlled by opening at least one valve to
cause pressure to drop in the combustion chamber.
21. A method according to claim 11, wherein: the variable is a
cylinder pressure gradient and in which a start of abnormal
combustion is detected by analyzing a sign of the gradient.
22. A method according to claim 12, wherein: the variable is a
cylinder pressure gradient and in which a start of abnormal
combustion is detected by analyzing a sign of the gradient.
23. A method according to claim 13, wherein: the variable is a
cylinder pressure gradient and in which a start of abnormal
combustion is detected by analyzing a sign of the gradient.
24. A method according to claim 14, wherein: the variable is a
cylinder pressure gradient and in which a start of abnormal
combustion is detected by analyzing a sign of the gradient.
25. A method according to claim 15, wherein: the variable is a
cylinder pressure gradient and in which a start of abnormal
combustion is detected by analyzing a sign of the gradient.
26. A method according to claim 16, wherein: the variable is a
cylinder pressure gradient and in which a start of abnormal
combustion is detected by analyzing a sign of the gradient.
27. A method according to claim 17, wherein: the variable is a
cylinder pressure gradient and in which a start of abnormal
combustion is detected by analyzing a sign of the gradient.
28. A method according to claim 18, wherein: the variable is a
cylinder pressure gradient and in which a start of abnormal
combustion is detected by analyzing a sign of the gradient.
29. A method according to claim 19, wherein: the variable is a
cylinder pressure gradient and in which a start of abnormal
combustion is detected by analyzing a sign of the gradient.
30. A method according to claim 20, wherein: the variable is a
cylinder pressure gradient and in which a start of abnormal
combustion is detected by analyzing a sign of the gradient.
31. A method according to claim 11, wherein: the variable is chosen
from among the following variables: cylinder pressure gradient,
energy release, temperature of cool gas or a logarithm of the
cylinder pressure.
32. A method according to claim 12, wherein: the variable is chosen
from among the following variables: cylinder pressure gradient,
energy release, temperature of cool gas or a logarithm of the
cylinder pressure.
33. A method according to claim 13, wherein: the variable is chosen
from among the following variables: cylinder pressure gradient,
energy release, temperature of cool gas or a logarithm of the
cylinder pressure.
34. A method according to claim 14, wherein: the variable is chosen
from among the following variables: cylinder pressure gradient,
energy release, temperature of cool gas or a logarithm of the
cylinder pressure.
35. A method according to claim 15, wherein: the variable is chosen
from among the following variables: cylinder pressure gradient,
energy release, temperature of cool gas or a logarithm of the
cylinder pressure.
36. A method according to claim 16, wherein: the variable is chosen
from among the following variables: cylinder pressure gradient,
energy release, temperature of cool gas or a logarithm of the
cylinder pressure.
37. A method according to claim 17, wherein: the variable is chosen
from among the following variables: cylinder pressure gradient,
energy release, temperature of cool gas or a logarithm of the
cylinder pressure.
38. A method according to claim 18, wherein: the variable is chosen
from among the following variables: cylinder pressure gradient,
energy release, temperature of cool gas or a logarithm of the
cylinder pressure.
39. A method according to claim 19, wherein: the variable is chosen
from among the following variables: cylinder pressure gradient,
energy release, temperature of cool gas or a logarithm of the
cylinder pressure.
40. A method according to claim 20, wherein: the variable is chosen
from among the following variables: cylinder pressure gradient,
energy release, temperature of cool gas or a logarithm of the
cylinder pressure.
41. A method according to claim 21, wherein: the variable is chosen
from among the following variables: cylinder pressure gradient,
energy release, temperature of cool gas or a logarithm of the
cylinder pressure.
42. A method according to claim 11, wherein: the measured and
estimated variables are compared.
43. A method according to claim 42, wherein: the measured and
estimated variables are compared using thresholds.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to combustion phase control of
an internal combustion engine. In particular, the present invention
is a method for detecting abnormal pre-ignition combustion at low
rpm and at high load in a combustion chamber of an internal
combustion engine. More specifically, but not exclusively, the
invention is a method applied to a "downsized" spark-ignition
engine functioning under very high loads.
[0003] 2. Description of the Prior Art
[0004] This type of engine has at least one cylinder comprising a
combustion chamber defined by the internal lateral wall of the
cylinder, by the top of the piston that slides in this cylinder and
by the cylinder head. Generally, a carbureted mixture is enclosed
in this combustion chamber and is subjected to a compression step
and then a combustion step under the effect of controlled ignition
by a spark plug. These steps are collectively described by the term
"combustion phase" in the following description.
[0005] It has been possible to confirm that this carbureted mixture
can be subjected to different types of combustion and that these
types of combustion are the source of different pressure levels, as
well as mechanical and/or thermal stresses, of which some can
seriously damage the engine.
[0006] The first combustion, called conventional combustion or
normal combustion, is the result of the propagation of the
combination of a carbureted mixture compressed by a prior engine
compression step. This combustion propagates normally along a flame
front starting from the spark generated by the spark plug and
involves no risk of harming the engine.
[0007] Another type of combustion is combustion with "knocking",
which results from undesirable self-ignition in the combustion
chamber. Thus after the compression step of the carbureted mixture,
the spark plug is actuated to allow ignition of the carbureted
mixture. Due to the effect of the pressure generated by the piston
and the heat released by the start of combustion of the carbureted
mixture, forceful and localized auto-ignition of part of the
compressed carbureted mixture occurs before the arrival of the
flame front issued from the ignition of the carbureted mixture by
the spark plug. Knocking leads to a local increase of the pressure
and the temperature and can cause destructive effects on the engine
and mainly at the piston, if repeated.
[0008] Finally, another type of combustion is abnormal combustion
due to pre-ignition of the carbureted mixture before the spark plug
initiates ignition of the carbureted mixture present in the
combustion chamber.
[0009] This abnormal combustion affects engines resulting from an
operation of "miniaturization," better known by the English term
"downsizing." This operation tends to decrease the size and/or the
cylinder of the engine while maintaining the same power and/or the
same torque as conventional engines. Generally, this type of
engines is mainly of the gasoline type and is highly
supercharged.
[0010] It has been possible to confirm that this type of abnormal
combustion occurs with high loads and generally during low rpm of
the engine when the heat of combustion of the carbureted mixture is
not optimum due to knocking. Taking into account the strong
pressures and the elevated temperature reached in the combustion
chamber by supercharging, starting of abnormal combustion can
occur, sporadically or in a continuous manner, before the moment
where the ignition of the carbureted mixture by the spark plug
takes place. This combustion is characterized by a first phase of
flame propagation that is timed too late in comparison to that of
conventional combustion. This propagation phase can be interrupted
by self-ignition which will involve a large majority of the
carbureted mixture present in the combustion chamber which is much
greater than that in the case of knocking.
[0011] In the case where this abnormal combustion is produced
repetitively, from engine cycle to engine cycle, and occurs
starting from a hot point of the cylinder, for example, it is
called "pre-ignition." If this combustion occurs in a violent
manner, randomly and sporadically, it is called "rumble"
("pre-ignition").
[0012] This latter abnormal combustion involves very elevated
pressure levels (120 to 250 bars), as well as an increase of the
thermal transfers that can involve partial or total destruction of
the moving engine parts, like the pistons or the rods.
[0013] The general methodology for processing this type of abnormal
combustion is diagrammed in FIG. 1. The first step is a prevention
phase (PP) for limiting to a maximum the chances of appearance of
the phenomenon. Then when prevention is not adequate to prevent the
phenomenon, a detection phase (PD) is performed for determining
whether or not there is a need to intervene in the cycle with a
corrective phase (PC) when pre-ignition has been detected.
[0014] The detection phase (PD) comprises a signal acquisition
phase followed by a signal processing phase making it possible to
detect the appearance of pre-ignition at high load to describe and
to quantify the pre-ignition at high load.
[0015] Patent Application EP 1.828.737 discloses a method for
detecting the appearance of pre-ignition at high load of the
"rumble" type. This method is based on the measurement of a signal
relative to the progress of the combustion and a comparison to a
signal threshold. The presence of an abnormal combustion of the
"rumble" type in the combustion chamber is detected when the signal
amplitude exceeds that of the signal threshold in a significant
manner. According to this method, the signal threshold corresponds
to the amplitude of the signal produced at the time of combustion
with knocking or at the time of normal combustion.
[0016] However, according to this method, the detection thus
implemented does not make it possible to act during the same cycle
as the detection. The corrective actions of this type of
pre-ignition are only implemented for the phenomenon that can
seriously damage the integrity of the engine.
[0017] The method described in French Patent 2,897,900 makes
possible more rapidly action after detection of the pre-ignition.
It is possible to act during the course of the same cycle as the
detection cycle of the phenomenon. In order to do this, the signal
threshold is calculated in advance, before the operation of the
engine, and then is stored in calculator data tables known as
maps.
[0018] However, the use of maps does not make it possible to
detect, at any time, that is in real time, the start of such a
phenomenon. Because of this fact, it is always possible that the
detection may occur too late. In addition, no quantification of the
trend of the pre-ignition can be implemented. Thus, the necessity
to not to apply a correction action rests solely on the comparison
of the two amplitudes at a given moment in time. Still, such a
phenomenon can actually start, then stop, without involving damage
to the engine and thus not require a corrective phase.
SUMMARY OF THE INVENTION
[0019] The invention is an alternative method for detecting, in
real time, the appearance of a pre-ignition phenomenon at high load
(of the rumble type), to characterize and to quantify it with
devices and systems currently used in engines, in such a way as to
take measures making possible prevention during the continuing
engine function in the course of the same cycle as that of the
detection. This detection and this quantification can be used at
any crankshaft angle. The method is based on processing of a
cylinder pressure measurement combined with modeling of the
cylinder pressure.
[0020] The invention concerns a control method of the combustion of
a. supercharged internal combustion engine with controlled
injection, in which abnormal combustion is detected in one
combustion chamber 14 of at least one cylinder 12 of the engine, by
a continuous pressure measurement P.sub.m(.alpha.) within the
cylinder. The method comprises the following steps: [0021] a)
choosing a physical model describing, as a function of the angle
.alpha. of rotation of the crankshaft of the engine, development of
the pressure in the cylinder during one combustion cycle without
any pre-ignition; [0022] b) estimating a cylinder pressure
P.sub.e(.alpha.) is, starting from the model and the measurement of
intake pressure; [0023] c) detecting a start of abnormal combustion
detected by comparing at least one first value of a variable
calculated using measurement of the cylinder pressure and at least
one second value of the variable calculated using the estimation of
the cylinder pressure; [0024] d) determining an amplitude of
pre-ignition by repeating steps b) and c) for a defined number of
crankshaft angles; and [0025] e controlling progress of the
abnormal combustion detected in the combustion chamber according to
the amplitude of the pre-ignition.
[0026] According to the invention, the physical model can describe
the progression of the pressure in the cylinder as a function of
the intake pressure and the combustion chamber volume of the
cylinder.
[0027] It is possible to control the sequence of the abnormal
combustion by introduction into the combustion chamber of an agent
containing fuel, water, or carbon dioxide. It is also possible to
control the sequence of the abnormal combustion by causing the
pressure to drop in the interior of the combustion chamber 14.
According to another embodiment, it is possible to control the
sequence of the abnormal combustion by opening at least one
additional valve to cause the pressure to drop in the interior of
the combustion chamber 14. Finally, according to another
embodiment, it is possible to control the sequence of the abnormal
combustion by opening at least one of the valves 24, 30 to cause
the pressure to drop on the inside of the combustion chamber
14.
[0028] According to the invention, the variable can be a cylinder
pressure gradient. Then the start of abnormal combustion is
detected by analyzing the sign of this gradient. It is also
possible to choose the variable from among the following variables:
a cylinder pressure gradient, an energy release, a cool gas
temperature, or the logarithm of the cylinder pressure.
[0029] Finally, according to the invention, it is possible to
compare several measured and estimated variables. This can be
carried out by means of thresholds.
BRIEF DESCRIPTION OF THE DRAWINGS
[0030] The other characteristics and advantages of the invention
will be seen from reading the description given below, referring to
the attached drawings, in which:
[0031] FIG. 1 shows the general methodology of processing abnormal
combustions of the pre-ignition type;
[0032] FIG. 2 shows an engine using the detection method according
to the invention;
[0033] FIG. 3 shows, as a function of the crankshaft angle .alpha.,
a measured cylinder pressure curve (R.sub.P) and a modeled cylinder
pressure curve (N.sub.P);
[0034] FIG. 4 illustrates the physical models used by the invention
according to different embodiments resulting from the cylinder
pressure;
[0035] FIG. 5 shows, as a function of the crankshaft angle a, a
measured cylinder pressure gradient curve (R.sub.dP) and a modeled
cylinder pressure gradient curve (N.sub.dP);
[0036] FIGS. 6A and 6D illustrate the sensitivity of cool gas to
pre-ignition wherein FIG. 6A represents the maximum energy release
(DEM) as a function of CA10 for a temperature of intake air
(measured in the plenum) of 30.degree. C. in gray and a temperature
of intake air (measured in the plenum) of 40.degree. C. in black,
FIGS. 6B and 6C represent the maximum energy release (DEM) as a
function of CA10 for a water temperature of 80.degree. C. (FIG. 6B)
and a water temperature of 100.degree. C. (FIG. 6C) with the
circled zone on the graph representing a pre-ignition zone, FIG. 6D
illustrates the connection between the water temperature and the
temperature of cool gas with the curves representing the trend in
the temperature of the cool gas (TGF) as a function of the
crankshaft angle (.alpha.) with the top curve corresponding to a
water temperature of 100.degree. C. and the lower one to a
temperature of 80.degree. C.; and
[0037] FIG. 7 represents the trend of log(P) as a function of
log(V) in a case of pre-ignition (black curve, N.sub.log) and
according to a model of a conventional combustion without
pre-ignition (gray curve, R.sub.log).
DETAILED DESCRIPTION OF THE INVENTION
[0038] In FIG. 2 illustrates supercharged internal combustion
engine 10 supercharged with controlled ignition, in particular a
gasoline type, comprising at least one cylinder 12 with a
combustion chamber 14, in which combustion of a mixture of
supercharged air and fuel occurs.
[0039] The cylinder comprises at least one means for supplying fuel
under pressure 16, for example, a fuel injector 18 controlled by a
slide valve 20 that opens into the combustion chamber, at least one
means for intake of air 22 with a valve 24 combined with an intake
pipe 26 ending at a plenum (not shown in the figure), at least one
means for exhausting the burnt gas 28 with a valve 30 and an
exhaust pipe 32 and at least one means for ignition 34, like a
spark plug, which makes it possible to generate one or more sparks
that make it possible to ignite the carbureted mixture present in
the combustion chamber.
[0040] The pipes 32 of the exhaust means 28 of this engine are
connected to an exhaust manifold 36, which itself is connected to
an exhaust pipe 38. A supercharging device 40, for example a turbo
compressor or a volumetric compressor, is placed on this exhaust
pipe and comprises an actuation stage 42 with a turbine powered by
exhaust gases circulating in the exhaust line and a compressor 44
that provides admission intake air under pressure into the
combustion chambers 14 by the intake pipes 26.
[0041] The engine comprises means 46a to measure the cylinder
pressure which is located within the cylinder 12 itself of the
engine. These measuring means are generally made up of a pressure
sensor that makes it possible to generate a signal representative
of the variation of the pressure in a cylinder.
[0042] The engine comprises means 46b for measuring the intake
pressure which is located in plenum 26b. These measuring means are
generally made up of an absolute pressure sensor, of the
piezoelectric type, which generates a signal representative of the
variation of the intake pressure in the intake plenum.
[0043] The engine also comprises a calculation and control unit 48,
called an engine computer, which is connected by conductors (some
of them bidirectional) to different elements and sensors of the
engine in such a way as to be able to receive different signals
emitted by these sensors, like the water temperature or the oil
temperature, in order to process them by computing and then control
the elements of this engine to ensure good operation.
[0044] Thus, in the case of the example shown in FIG. 2, the spark
plugs 34 are connected by conductors 50 to the engine computer 48
to control the time of sparks igniting the carbureted mixture. The
cylinder pressure sensor 46a is connected by a line 52 to this same
engine computer to send signals thereto representative of the
variation of the pressure in the cylinder and the control slide
valves 20 of the injectors 18 are connected by conductors 54 to the
computer 48 to control the injection of the fuel into the
combustion chambers. Means 46b are also connected by a line 53 to
the engine computer 48.
[0045] Within such an engine, the method according to the invention
makes it possible to detect the appearance of a pre-ignition
phenomenon at high load (of the rumble type), to describe and to
quantify it. This detection and this quantification can be carried
out at any crankshaft angle.
[0046] The method is based on a processing of a cylinder pressure
measurement combined with a modeling of the cylinder pressure
(signals emitted by the cylinder pressure sensor which are
representative of the state of combustion). According to one
embodiment, the method comprises the following steps: [0047] 1--the
pressure in the cylinder is modeled; [0048] 2--the pressure in the
cylinder is measured; [0049] 3--the start of abnormal combustion is
detected by comparing the measured pressure cylinder to the modeled
cylinder pressure; and [0050] 4--the progress of the abnormal
combustion which is detected in the combustion chamber is
controlled.
1--Modeling the Pressure in the Cylinder
[0051] The cylinder pressure in the course of the compression phase
can be modeled for each of the engine cycles by using the
hypothesis of polytropic compression:
PV.sup.n=cte
[0052] where P is the pressure in the cylinder and V the volume of
the combustion chamber of the cylinder. These two parameters
naturally vary as a function of the rotation angle of the
crankshaft .alpha..
[0053] The relationship between the volume of the combustion
chamber and the angle of rotation of the crankshaft a is called the
"law of engine volume" V(.alpha.). This law is a function of the
geometric characteristics of the engine (stroke, cylinder bore,
volumetric compression ratio and rod length). The dead volume Vm
corresponds to the minimum volume of the chamber (at top dead
center). It is noted that V.sub.PMB, the volume of the combustion
chamber at bottom dead center, that is the maximum volume, is
reached two times in the combustion cycle (a first time at the end
of the intake phase and a second time at the end of the pressure
reduction phase).
[0054] By using this ratio for any crankshaft angle and the same
ratio for the intake pressure P.sub.adm (moment at which bottom
dead center is reached), it is possible to estimate the cylinder
pressure P.sub.e(.alpha.) during conventional combustion, that is
without any pre-ignition phenomenon, using the following model:
P e ( .alpha. ) = P adm ( V PMB V ( .alpha. ) ) n ##EQU00001##
[0055] The law of engine volume V(.alpha.) is known. The pressure
during the intake phase is also known due to the means 46b for
measuring the intake pressure. The exponent n, called the
polytropic exponent, is also known. Thus it is possible to estimate
a "theoretical" cylinder pressure, that is the pressure that must
be present in the cylinder if no pre-ignition has occurred
throughout the compression.
[0056] It should be noted that the pressure during the intake phase
theoretically corresponds to the pressure in the cylinder at the
moment of intake of the carbureted mixture. This pressure is
measured in the manifold. It is possible to replace this pressure
by the pressure in the cylinder at the start of compression (that
is at the end of intake), tuned on the absolute pressure measured
at the intake in the manifold at the end of the intake phase (it is
assumed that equilibrium is achieved at the end of the intake phase
and at that moment: P.sub.adm=P).
2--Pressure Measurement in the Cylinder
[0057] The measurement of the cylinder pressure P.sub.m(.alpha.) is
performed using means 46a for measuring the cylinder pressure. The
instrumentation of the cylinders for a pressure measurement is more
and more usual on vehicles.
3--Comparison of the Measured and Modeled Cylinder Pressures
[0058] To determine whether pre-ignition is in the course of
occurring, the measured cylinder pressure P.sub.m(.alpha.) is
compared to the modeled cylinder pressure P.sub.e(.alpha.). This
comparison can thus be implemented at each crankshaft angle. This
thus makes it possible to very rapidly detect the least deviation
of the measured cylinder pressure in comparison to the theoretical
cylinder pressure (modeled). By performing this comparison, over
several crankshaft angles, it is possible to describe this
deviation: the deviation can increase slowly, rapidly, stabilize,
decrease, etc. As a function of the variation in this deviation,
the pre-ignition is thus described and it is measured to decide
what corrective actions to be taken, or not.
[0059] FIG. 3 shows a measured cylinder pressure curve (R.sub.P),
in black, and a modeled cylinder pressure curve (N.sub.P) according
to the model described above, which describes a cylinder pressure
curve for conventional combustion. The abscissa indicates the
crankshaft angle .alpha.. The dotted vertical line indicates the
moment at which the controlled ignition takes place. It can be
confirmed that pre-ignition leads to excessive thermodynamic
conditions, which puts the integrity of the engine at risk.
However, it should be noted that the detection of a deviation
between the measured and modeled cylinder pressures can be carried
out very early on in the combustion cycle.
[0060] It is also possible to quantify these deviations in such a
way as to determine at what time in the combustion cycle it is
important to intervene.
[0061] In order to do this, it is possible to determine the
thresholds, starting from a time at which rumble type pre-ignition
is considered to be in the course of occurring and an indication
that intervention is necessary.
[0062] For example, it is possible to define the following
thresholds at each crankshaft angle
[0063] an absolute cylinder pressure not to exceed
P.sub.m(.alpha.)<S.sub.1
[0064] a pressure deviation not to exceed
P.sub.m(.alpha.)-P.sub.e(.alpha.)<S.sub.2
[0065] a pressure ratio not to exceed
P.sub.m(.alpha.)/P.sub.e(.alpha.)<S.sub.3
[0066] The thresholds S.sub.1, S.sub.2, and S.sub.3 are defined
before the engine operation as for example on the test bench.
[0067] According to an advantageous embodiment of the invention,
these thresholds can evolve in the course of the engine operation.
For example, it is possible to consider these thresholds to take
account for the aging of the vehicle. Indeed, the fouling of the
engine can be an aggravating factor with regard to the sensitivity
of the engine to pre-ignition. According to the invention, this
phenomenon is taken into account by arbitrarily setting the
thresholds so they are more severe (for example by reducing the
pressure limit) while regularly closely observing the behavior of
the engine to periodically adjust these thresholds. The necessary
adjustment level can be determined during the phase of tuning the
engine by simulating accelerated aging of the engine, for example
by inducing significant fouling with the use of a specific
procedure. Generally an action is taken on the engine temperature,
but also on the injection and ignition phases, to decrease the
combustion and thus to generate carbon deposits on the walls of the
combustion chamber identical to that which occurs during natural
aging of the engine. Each experimenter is thus free to define the
correspondence between an intentional accelerated aging and the
natural aging of the engine involved. Finally, the previously set
thresholds evolve in a manner that is inversely proportional to the
aging of the vehicle, due to a correction coefficient K.
S ' = S * K ##EQU00002## where K .alpha. 1 odometer reading
##EQU00002.2## or even K .alpha. 1 .theta. odometer reading for
example , ##EQU00002.3##
[0068] The comparison of the two signals can naturally be carried
out at several crankshaft angles. An early detection during the
compression phase is preferable in any case, on one hand to
maintain a margin sufficient for intervening in the cycle and on
the other, since the most violent pre-ignitions start at the time
of this compression phase.
4--Control of Abnormal Combustion
[0069] By means of this comparison, the engine computer can detect
the start of an abnormal combustion of the "rumble" type or of the
"pre-ignition" type in the combustion chamber.
[0070] In the case of abnormal combustion, the computer then
triggers the actions necessary to control this combustion in order
to prevent the continuation of such combustion.
[0071] To control abnormal combustion, not only is it possible to
manage the progress of combustion to prevent a serious increase in
destructive pressure, but it is also possible to completely stop
such combustion, such as by damping.
[0072] Preferably, the control of the combustion is implemented by
a reinjection of the fuel at a crankshaft angle determined by the
injectors 18. More specifically, the computer controls the slide
valves 20 in such as a way that for the injector of the cylinder
which is concerned it is possible to introduce into the combustion
chamber a quantity of fuel in liquid form. The quantity of fuel
reinjected depends on the make-up of the engine and can be from 10%
to 200% of the quantity of fuel initially introduced into this
combustion chamber. The reinjected fuel counters the flame that
starts to deploy at the time of abnormal combustion. This
reinjection makes it possible either to extinguish this flame or to
damp the flame by increasing the richness of the carbureted
mixture. Besides that, the injected fuel in liquid form uses the
heat present around this flame to evaporate and the temperature
conditions around the flame decrease while the combustion of the
carbureted mixture and above all its auto-ignition is retarded.
[0073] After this injection of fuel, the pressure in the cylinder
increases, but less forcefully. This pressure then decreases to
achieve a level compatible with the pressure level of conventional
combustion.
[0074] By using this mechanism, any development of abnormal
combustion with high combustion speed and elevated pressure is
prohibited. Naturally, the use of means for controlling abnormal
combustion occurs at each cycle during which such combustion is
detected by the computer.
[0075] The actions of the method as described above can be combined
with other slower actions, such as closing the throttle valve to
prevent the pressure conditions of the combustion chamber from
being favorable for abnormal combustion in the following
cycles.
[0076] The present invention is not limited to the implementation
examples described above, but encompasses all variants and all
equivalents.
[0077] In particular, and without departing from the scope of the
invention, other agents for stopping abnormal combustion can be
introduced into the combustion chamber. Thus these agents can be
water in the form of vapor or liquid, or carbon dioxide. In this
case, the engine comprises specific additional injectors for
introduction of these agents in combination with a dedicated
circuit (pump, tank, etc.).
[0078] It is also possible to envision controlling abnormal
combustion by lowering the internal pressure of the combustion
chamber by discharging pressure by opening a discharge valve. This
discharge valve can be either an additional valve or the intake
valve 24 and/or the exhaust valve 30.
[0079] In addition, the present invention can also concern a
controlled-ignition engine with indirect injection. In this case,
the control of the progress of abnormal combustion will be by the
use of a specific injector (fuel, water, CO2) as mentioned above or
by closing the valve.
Variants
[0080] An embodiment has been described that uses a model of
cylinder pressure directly. According to other embodiments, it is
possible to use derivative models (FIG. 4). Indeed, several signals
can be used to detect the pre-ignition in real time, for example by
working on: the gradient of the cylinder pressure, release of
energy, the temperature of the cool gas, or even by working on the
diagram log P/log V.
Cylinder Pressure Gradient (FIG. 5)
[0081] As a general rule, the conditions of appearance of
pre-ignition (low engine rpm and high loads) occur when the
ignition by the spark from the spark plugs is much more delayed
during the pressure reduction phase in such a way as to prevent
knocking. The cylinder pressure curve then shows the appearance of
a first peak connected with the compression and a second offset
peak connected with the combustion (FIG. 3). It is thus possible to
detect the pre-ignition based solely on the sign of the cylinder
pressure gradient. If the sign of the cylinder pressure is positive
before the spark has been produced, it involves a pre-ignition.
[0082] In the same manner as for cylinder pressure, detection
thresholds on the derivative of the cylinder pressure can also be
defined at each crankshaft angle (the index "e" indicates an
estimate and the index "m" a measurement): [0083] an absolute
pressure gradient not to exceed dP.sub.m(.alpha.)<S.sub.4 [0084]
a deviation not to exceed dP.sub.m(.alpha.)-d
P.sub.e(.alpha.)<S.sub.5 [0085] a ratio not to exceed
dP.sub.m(a)/dP.sub.e(a)<S.sub.6
Discharge of Energy
[0086] The derivative of the cylinder pressure can also be used to
calculate a simplified energy discharge .delta.Q:
dU = .differential. Q + .differential. W dU = m C v dT
.differential. W = - P dV P V = m r T r = C p - C v s = C p C v }
.differential. Q = s s - 1 P dV + 1 s - 1 V dP ##EQU00003##
[0087] This simplified energy discharge can then also be used to
define a threshold (the index "e" indicates an estimate and the
index "m" a measurement) [0088] by an absolute energy discharge not
to exceed .delta.Q.sub.m(.alpha.)<S.sub.7 [0089] by an energy
discharge deviation
.delta.Q.sub.m(.alpha.)-.delta.Q.sub.e(.alpha.)<S.sub.8 [0090]
by an energy discharge ratio
.delta.Q.sub.m(.alpha.)/.delta.Q.sub.e(.alpha.)<S.sub.9 [0091]
by calculating the advance indicators of the combustion, indicated
CAX, and by comparing them to the same indicators calculated using
the theoretical cylinder pressure evaluated by modeling. X
designates the percentage of advance of the combustion. The angle
CA10 corresponds, for example, to the angle where 10% of the energy
introduced has been discharged or, according to the convention
used, with 10% of the total energy released.
Temperature of the Cool Gas (FIGS. 6A-6D)
[0092] The average temperature of the cool gas T (air and fuel) is
a parameter that presents the advantage of having a great influence
on the sensitivity of the combustion at pre-ignition. Still, this
temperature can be estimated using several other variables like
temperature in the intake manifold (FIG. 6A), the quantities of air
and of fuel admitted and the cylinder pressure. Thus it is possible
to detect, even anticipate, a pre-ignition by placing a threshold
at this temperature of the cool gas. Early detection of
pre-ignition and good anticipation make it easy to provide more
time for triggering a remedial action in the cycle itself.
[0093] FIG. 6A represents the maximum energy release (DEM) as a
function of CA10 for a temperature of the intake air (measured in
the plenum) of 30.degree. C. in gray and a temperature of the air
intake (measured in the plenum) of 40.degree. C. in black. The
circled zone on this graph represents a zone of pre-ignition.
[0094] FIGS. 6B and 6C represent the maximum energy release (DEM)
as a function of CA10 for a water temperature of 80.degree. C.
(FIG. 6B) and a water temperature of 100.degree. C. (FIG. 6C). The
circled zone on this graph represents a pre-ignition zone.
[0095] FIG. 6D illustrates the connection between the temperature
of the water and the temperature of the cool gas. The curves
represent the trend in the temperature of the cool gas (TGF) as a
function of the crankshaft angle (.alpha.). The top curve
corresponds to a water temperature of 100.degree. C. and the bottom
one to a temperature of 80.degree. C.
[0096] This average temperature of the cool gas T.sub.e(.alpha.)
can be calculated simply by using the perfect gas state
equation:
P V = m r T T e ( .alpha. ) = P e ( .alpha. ) V ( .alpha. ) m r
##EQU00004##
[0097] The mass of the mixture m may be known from the engine or by
direct measurement using a flow meter or by models that evaluate,
in real time, the air feed entering using pressure measurements of
the intake line.
[0098] The detection threshold of the temperature can also be
defined in three ways at a given crankshaft angle (the index "e"
indicates an estimate and the index "m" a measurement): [0099] by
an absolute temperature not to be exceeded
T.sub.m(.alpha.)<S.sub.10 [0100] by a temperature range
T.sub.m(.alpha.)-T.sub.e(.alpha.)<S.sub.11 [0101] by a
temperature ratio T.sub.m(.alpha.)/T.sub.e(.alpha.)<S.sub.12
Diagram log P/log V (FIG. 7)
[0102] The variables log(P) and log(V) offer the advantage of
simplifying the representation of the trend in the cylinder
pressure in the course of the engine cycle.
PV*=cte
log P +n.log V=cte
log P=cte-n.log V
[0103] FIG. 7 represents the trend of log(P) as a function of
log(V) in a case of pre-ignition (black curve, N.sub.log) and
according to a modeling of the conventional combustion without
pre-ignition (gray curve, R.sub.log).
[0104] The advantage of this representation is in the exploitation
of the linearity that connects log P and log V. Indeed, this
linearity makes it possible to gain predictive capacity since the
slope followed by the compression (Comp) up to PMH can be known
from the initial instant of this compression. Thus it is possible
to model the theoretical pressure by calculating the slope n using
the measurements performed at the start of compression.
[0105] In addition, this method makes it possible to detect not
only the pre-ignitions that occur during compression, but also
those that occur during pressure reduction (Def) since this linear
relationship also exists during pressure reduction. In the case of
an ignition (All) at the spark plug offset during the pressure
reduction, it is thus possible to predict the path that the
cylinder pressure must follow up to this ignition.
[0106] It should be noted, the ignition at the spark plug is a very
high load that must be offset during the pressure reduction to
prevent the appearance of knocking. While negative in terms of
yield, this offset is very effective for preventing knocking. There
a cylinder pressure curve with two peaks is found: a first peak
corresponding to the pure compression of the mixture and a second
peak corresponding to the increase in pressure generated by the
combustion (FIG. 3). Under these conditions, the pre-ignition is
triggered either during compression (the most critical cases) or
during the pressure reduction after the first peak of
compression.
[0107] The threshold can then be defined by a deviation between the
curve representing the log of the measured cylinder pressure and
the curve representing, the theoretical cylinder pressure
(modeled): [0108] by an absolute term log(P) not to exceed log
P.sub.m(.alpha.)<S.sub.13 [0109] by a deviation not to exceed
log P.sub.m(.alpha.)-log .sub.Pe(.alpha.)<S.sub.14 [0110] by a
ratio not to exceed log P.sub.m(.alpha.)/log
P.sub.e(.alpha.)<S.sub.15
[0111] According to one embodiment, for all the ratios between an
experimental variable and a modeled variable, in particular those
that have the risk of canceling each other, the ratio is made less
unstable, by regularizing the expression with one or several
constant terms (in this case P0.sub.m and P0.sub.e), avoiding the
cancellation or the calculation and also making it possible to
compensate a strict non-linearity among the variables. For
example:
log(P.sub.m(.alpha.)+P.sub.m.sup.0)/(P.sub.e(.alpha.)+P.sub.e.sup.0)<-
S.sub.15
[0112] These terms are determined a priori as a function of the
expected variable.
[0113] In an advantageous manner a variable is not used, but rather
a combination of variables, for example P and V.
[0114] Finally, in order to limit the impact of the localized
fluctuations, it is interesting to carry out comparisons with the
thresholds, not only with the variable recorded at an angle
.alpha., but with estimations of these variables at a certain
angular range (small or on the same order as the minimum duration
necessary to estimate the passing of a threshold). If three angular
measurements are taken in succession, P(-1) P(0) P(+1) for example,
an estimation of P at point 0 can be obtained by taking the average
of [P(-1) P(0) P(+1)], their median value, their maximum or any
combination with a weighting of these values. This is useful for
the calculation of the derivative, for example. This calculation
can be carried out in a recursive manner, that is by reusing at
point 0 the preceding measurement at point -1 in [P(-2) P(-1)
P(0)].
Application
[0115] Thus, at the time the engine function as described in
relationship with FIG. 2, the means for measuring cylinder pressure
46a records the variation in this pressure within cylinder 12. This
information is sent in the form of a signal by line 52 to the
engine computer 48. This computer estimates, for example at each
crankshaft angle, the cylinder pressure by means of a physical
model and compares the modeled and measured cylinder pressures
using the threshold values, for example. This comparison allows the
engine computer to determine the presence of the start of abnormal
combustion of the rumble type in the combustion chamber. The engine
computer then sends the instructions for control using the fuel
feed under pressure 16 by way of the conductors 54 to modify the
injection parameters in a manner such that this abnormal combustion
of the rumble type is not reproduced during the following
cycles.
[0116] Thus, according to the invention, the detection of
pre-ignition takes place starting from its initiation in such a way
as to be able to quantify and define its progress in real time. The
detection can be carried out for any crankshaft angle of each
engine cycle. The detection thus takes place well before the
pre-ignition leads to thermodynamic conditions that are critical
for harming the integrity of the engine. The invention thus makes
it possible, on one hand, to judge whether this pre-ignition is
critical for harming the engine and on the other, to act in the
same cycle as the detection to eliminate or decrease it. The
detection is based on a comparison of signals connected to the
cylinder pressure with the modeled signals corresponding to the
values obtained for these same signals in the case of conventional
combustion, that is without appearance of pre-ignition, and does so
for each crankshaft angle of each engine cycle, thus making
possible an extremely precise detection of the phenomenon, a
quantification, and a rapid action to control the phenomenon.
* * * * *